Audience effect is context dependent in Siamese fighting fish, Betta splendens

Investigations of communication networks in animals have focused primarily on determining whether animals extract information from peripheral contests (eavesdropping) or respond to the presence of bystanders (audience effect). The possibility that an animal's response to being watched might be context dependent, however, has been explored in far less detail. This study investigated the influence of two contexts, exposure to audiences of different sexes and presence or absence of a nest, on the aggressive behavior of interacting male Siamese fighting fish, Betta splendens. Males interacted in the presence (male, female) or absence of an audience in three different nest conditions (0, 1, or 2 nests). Audience sex and territorial status influenced aggressive behavior in the interacting males, but a strong audience x nest interaction also was uncovered. Males were more aggressive when neither male had a nest and a male audience was present than when a female or no audience was present. Males also were more aggressive when only one male had a nest and a male audience was present than when a female or no audience was present. When both males had nests and a male audience was present, however, males were less aggressive than when only one male or neither male had a nest. In sum, aggressive behavior was influenced by the interaction between audience and nest; neither nest nor audience alone was sufficient to explain the results. Male Siamese fighting fish alter their behavior based on both external cues, the sex of the audience, and internal cues, reproductive state and resource possession. Our results emphasize the importance of considering aspects of an animal's environment when examining audience effects and communication networks in general.